The present invention relates to vessel or sheet for growing (hereinbelow, the term xe2x80x9cgrowxe2x80x9d is used in a meaning such that it also includes the germination of a plant, and the growth thereof after the germination) a plant, a support for cultivating a plant, and an agent for modifying (or reforming) soil, which are suitably usable for tissue culturing or the germination of a seed and the growth thereof after the germination, and the growth of a plant in farm cultivation; and a method of growing (in the present specification, the term xe2x80x9cgrowthxe2x80x9d is used in a meaning such that it also includes germination and growth after the germination) a plant, while using a gel-like support substantially as it is which has been used in the artificial culturing, whereby a plant can be cultivated in an environment wherein aeration or ventilation is not restricted (e.g., in farm cultivation).
More specifically, the present invention relates to a vessel or sheet for growing a plant (hereinbelow, this term is used in a meaning such that it also includes xe2x80x9cseedxe2x80x9d), which enables easy transfer of the plant, the promotion of the germination or growth of the plant, and marked reduction in the necessity for strict control of water, etc.
a support to be used for supporting or carrying a plant in the cultivation of the plant; and a soil-modifying agent for supporting or carrying a plant in the cultivation of the plant in combination with another plant-supporting carrier (such as soil), whereby the physical, chemical and microbiological properties of the carrier can be improved or modified on the basis of the application of such a soil-modifying agent to another carrier such as soil); and a method of growing a plant which enables continuous growth of a plant from the culturing to cultivation thereof; and particularly, a method of continuously growing a plant wherein at the time of the transfer from the culturing thereof in a vessel into farm cultivation thereof, the support (or planting material) which has been used in the culturing of the plant can also be used as it is in the cultivation thereof, thereby to omit or simplify the transferring step for the plant, to prevent the physical damage to the root thereof, and to enable the smooth growth of the plant after the transfer thereof into the cultivation step.
In the present specification, xe2x80x9cculturexe2x80x9d (or culturing) of a plant refers to the growth or multiplication of the plant under a condition (mainly in a vessel) such that the aeration or ventilation into the plant-growing system is controlled or limited; and xe2x80x9ccultivationxe2x80x9d of a plant refers to the growth or multiplication of the plant under a condition (mainly in a greenhouse or open-air field) such that the aeration or ventilation into the plant-growing system is not limited. With respect to such definition of the culture, it is possible to refer to xe2x80x9cTechnique in Plant Tissue Culturingxe2x80x9d edited by Takeuchi et al., Page 1 (1983), Asakura Shoten; and xe2x80x9cIwanami Biological Dictionaryxe2x80x9d (3rd edition) edited by Yamada et al., Page 1006 (1983), Iwanami Shoten.
In recent years, it has attracted much attention to develop a technique for growing or regenerating a plant having a character or trait suitable for an intended purpose. Among these growing and regenerating techniques, a plant tissue culture technique, i.e., a technique wherein a part of a plant is separated from the main body thereof, and is grown in the inside a culturing vessel has particularly attracted much attention, since it enables the mass multiplication of a genetically identical clone in a short period of time. (Kiyoshi Okawa xe2x80x9cGeneral Introduction to Horticultural of Flowersxe2x80x9d, page 54, 1995, Yokendo). Heretofore, in the production of a plant (mainly, a plantlet) using a plant tissue-culturing technique, agar gel has been used as a support therefor. However, the agar gel has a characteristic such that it hardly absorb water content again, after it discharges water content due to the evaporation of water or the absorption of water into the plant. Particularly, in an open-system cultivation environment such as farm cultivation, the water content-retaining function of the agar and the plant-retaining function thereof as a gel are rapidly decreased. Accordingly, it is naturally impossible to use the agar gel as the support (or planting material) in the open-system farm cultivation.
From such a viewpoint, it is necessary to remove the agar gel at the time at which a plantlet is transferred from the culture thereof in a vessel into the farm cultivation thereof. However, it is inevitable to manually conduct a step of removing the agar gel one by one with respect to the plantlet, and therefore such a removing step not only requires much labor and long time, but also poses some problems such that it damages the root of the plantlet, is liable to cause a root decay (or root rot) phenomenon, etc.
On the other hand, in the case of the culture of a very small plantlet (minute plantlet), a saccharide is generally added into the liquid culture medium to be used for the culture. The reason for this is that, in general, such a minute plantlet does not have an organ such as albumen of a seed, leaf and stem portion thereof for conducting a photo-synthesis reaction is not sufficiently developed, and therefore it is necessary to add a carbon source which the minute plantlet can absorb directly. In addition to the case of the tissue-cultured plantlet, in a case of a seed having no albumen such as that of an orchid (Orchidaceae) plant, a minute plantlet which has been germinated in a vessel is subjected to a saccharide-involving (or saccharide-relating) culture process for a similar reason. However, since the saccharide which has been added into the plant-growing system promotes the propagation of various germs, it is substantially impossible to use the agar gel containing a saccharide as it is in an open-system (non-sterilized) environment such as farm cultivation.
As described above, in a case where the conventional method of growing a plant by using agar gel, it is substantially impossible to continuously grow the plant from the culture thereof to farm cultivation thereof (by using the support used for the culture as it is), and therefore the step of removing the agar is required. In addition, since such a agar-removing step must be conducted by using manual operations, a considerable period of time is required, and further, the step has problems such that it damages the root of the plant, and various germs are liable to propagate due to the presence of the remaining agar gel so as to cause a root decay phenomenon.
In addition to the above-mentioned problem of the transfer from the xe2x80x9cculturexe2x80x9d to the xe2x80x9ccultivationxe2x80x9d, in the course of plant growth, it is also an important subject to control the amount of the supply of water content, a nutrient, etc., to the plant.
In view of the physiology of a plant, xe2x80x9cwaterxe2x80x9d is one of the environmental factors which exerts the greatest influence upon the growth of the plant, and particularly, it is an element essential for the photo-synthesis. The absorption of the water content, which is an extremely important environmental factor, is mainly concerned with the transpiration due to xe2x80x9cstomataxe2x80x9d as openings of the back surface of a leaf of the plant.
More specifically, when the water content of cells constituting a plant is decreased by the transpiration of water, the water content in the plant assumes a non-equilibrium state, and the plant absorbs water content in soil through the root thereof on the basis of the xe2x80x9ctranspiration pressurexe2x80x9d as an action for retaining the non-equilibrium state in an equilibrium.
The above-mentioned stoma also has a function of taking CO2 in, which is necessary for the photo-synthesis, from the air. However, since the water content in the mesophyll cells, wherein the photo-synthesis is mainly to be conducted, is transpired due to the presence of the openings of the stomata, the water content in the mesophyll cells is required to be supplemented promptly. In other words, water must be supplied plentifully to the plant along with the absorption of solar energy and CO2 so that plant conducts the photosynthesis more effectively.
In the daytime environment wherein the temperature is high and the light quantity of the sunlight is large, when the water content which a plant can utilize is insufficient in the cultivating soil, or when the water-absorbing ability of the root-of the plant is lowered, the water content in the plant is decreased, and the water content in the mesophyll cells wherein the photo-synthesis is mainly to be conducted is also decreased. As a result, not only the photo-synthesis is markedly inhibited, but also the photo-synthesis product is markedly decreased so that the growth of the plant per se is suppressed, and there is a danger such that the plant is withered to death in the course of time. Further, when the water content in soil becomes insufficient, the concentration of mineral salts contained in the soil is increased. On the contrary, when the water content in soil becomes excessive, the supply of oxygen to the root of the plant becomes insufficient. In both of these cases, there is a fear such that the plant is adversely affected.
On the other hand, xe2x80x9ctemperaturexe2x80x9d is also one of the environmental factors which greatly affects the growth of a plant. For example, the absorption of mineral salts through the root of a plant is increased along with an increase in temperature, but the absorption will have a maximum when the temperature reaches at a certain value, and is sharply decreased at a higher temperature than such a value. It is known that the maximum value of the mineral salt absorption is present in the neighborhood of 40xc2x0 C. in most of the plants. The absorption of nutrients in a lower temperature region is mainly based on a simple diffusion phenomenon, but the ratio of active nutrient absorption based on a biochemical absorption process is increased along with an increase in temperature. In a high-temperature region of 40xc2x0 C. or more, the deactivation of an enzyme system relating to the biochemical absorption process is regarded as a cause of sharp decrease in the nutrient-absorbing rate. Accordingly, the control of water in the cultivating soil and the control of the amount and concentration of nutrients with respect to a temperature change is very important technique for the cultivation of a plant.
On the other hand, from a viewpoint of technique of crop production, cultivation in open-air field has heretofore been conducted in a natural (or non-artificial) environment with respect to crops such as grain plant, vegetables, flowering plants, and fruit trees. However, inter open-air field cultivation, since the production amount of the crops are greatly varied due to a violent change in temperature during four seasons, unstable rainfall conditions, etc., the development of the agriculture as an industry has rather been limited.
In recent years, the cultivation of crops in facilities such as greenhouse has been popularized for the purpose of overcoming the above-mentioned problems in the open-air field cultivation or for the purpose of shipping the crops throughout one year (in any season constituting one year). As a result, it becomes possible to supply agricultural products stably.
However, in the facility cultivation, the production cost of the crops inevitably becomes high. The reason for this is that, in the facility cultivation, the facility-and-equipment investment becomes very large, which is necessary for the construction of the facility main body such greenhouse, the internal equipment such as watering apparatus in the facility, or environment-controlling instrument for regulating the temperature, concentration of nutrients, light intensity, etc., in the facility. On the other hand, in the above-mentioned open-air field cultivation, in many cases, there is required a large investment in the irrigation and watering facilities, etc., for the purpose of overcoming the influence of sudden changes in the natural environment.
In general, the use of chemical-type fertilizers in place of organic-type fertilizers has been considered as one of the important factors which have supported the development of-modern agriculture. However, the ratio of the chemical-type fertilizer which is to be actually absorbed into a plant is considered to be usually below 30%. Accordingly, in recent years, there is a fear such that soil is deteriorated and the environment is polluted globally due to the use of the chemical-type fertilizer, and the natural resources to be used as the raw material for producing the chemical-type fertilizer are even exhausted.
In order to solve the above-mentioned problems, there has strongly been demanded a method of effectively applying a fertilizer to a plant, or an improvement in xe2x80x9ccarrier for supporting a plantxe2x80x9d such as soil with which a fertilizer is effectively applied to a plant.
In recent years, in addition to the above-mentioned problem in the xe2x80x9ccarrierxe2x80x9d, the improvement in a xe2x80x9cvesselxe2x80x9d for growing a plant also becomes an important subject in the field of the plant growth.
Heretofore, the transfer of a plant is required to be conducted by long-term troublesome manual operations. Further, there are pointed out various problems such that the above-mentioned manual operations damage the plant, or they considerably impair the initial (or early-phase) growth of the plant after the transfer operation, etc. From such a viewpoint, it has strongly been desired to automate the transfer operation of a plant, to reduce the transferring damage (or rooting damage) at the time of the transfer operation, or to promote the initial growth of the plant after the transfer operation.
In addition, the conventional vessel for growing a plant has a problem such that it is liable to deteriorate the physical environment of the rhizosphere of the plant. In general, when the root of a plant is extended to the wall surface of a vessel, it is further extended downward along the wall surface, and when the root reaches the bottom surface of the vessel, it is extended so as to be formed into a coil-like shape along the bottom surface in many cases. It is considered that such a phenomenon of root extension is based on the property of the root of extending in the direction of the gravity, and the property thereof of extending due to the contact surface stimulus to be applied to the root. On the other hand, in the cultivation of a plant using a vessel, it has heretofore been investigated particularly intensively to find what kind of supporting carrier (such as soil) is optimum in view of the growth of the plant. Accordingly, the investigation of the physical environment of internal surface of the vessel has been insufficient.
In general, the physical environment of the interior of the carrier for retaining a plant is utterly different from that of the internal surface of the vessel. In the latter environment, i.e., in the neighborhood of the internal surface of the vessel, since the difference in the temperature (hot and cold) and humidity (dry and wet) is large, there is particularly liable to occur a problem such that the growing point of the root which contacts the internal wall surface, or an intermediate portion of the root which is extended along the internal wall surface, causes browning and fatal withering.
Heretofore, specific examples of the vessel or sheet to be used for the growth of a plant, include unglazed (earthenware) pots, plastic pots, vinyl pots, planters, trays for xe2x80x9cplug-typexe2x80x9d plantlet, trays for plantlet, paper pots, vinyl sheets, etc. In any of these vessels, when the material of the vessel (such as usual plastic material) is one which intercepts the circulation of water or outside air, the place in the neighborhood of the internal wall surface of the vessel is a place wherein water is liable to be accumulated, and a root decay phenomenon is liable to occur. On the other hand, when the material of the vessel is one which enables the circulation of outside air (such as unglazed earthenware and paper), on the contrary, the place in the neighborhood of the internal wall surface of the vessel is a place wherein water is liable to be insufficient, and the growth of the plant is liable to be markedly hindered.
In addition, the vessel to be used in the farm cultivation is generally one having an open-system portion in the upper and lower parts thereof. Accordingly, after a watering operation, the supplied water is promptly drained from the lower part of the vessel through the plant-supporting carrier, thereby to cause problems such as the necessity for excessive watering operations and the flowing-out of nutrients. Further, in the case of a vessel to be used in general homes, a xe2x80x9cpanxe2x80x9d for receiving water, etc., drained from the lower part of the vessel is required.
Further, when such an open-type vessel is used, since the amount of water immediately before the watering operation is liable to be sharply decreased suddenly, the concentration of nutrients is sharply increased, whereby the plant can be adversely affected. On the other hand, when the amount of water to be used in the watering operation is increased, the frequency of the watering operation is increased, or the conventional vessel and soil having a high water-retaining property are selected for the purpose of improving such a situation, the accumulation of excessive water lasting immediately after the watering inhibits the supply of oxygen to the root, and microorganisms adversely affecting the plant are propagated, whereby a root decay phenomenon is liable to occur. On the contrary, when the plant-growing system is dried for the purpose of promoting the supply of oxygen, or of suppressing the propagation of microorganisms adversely affecting the plant, the above-mentioned problems of a decrease in the water content and the concentration of nutrients become severer, and therefore a fertilizer must be supplied to the plant in a smaller amount than that of the fertilizer required by the plant.
As described above, the present plant cultivation using a plant-growing vessel is caught in a vicious circle or falls into a self-contradiction, and therefore such a condition makes it difficult to cause a plant to exhibit its growing power to the maximum.
Further, the upper portion of the above-mentioned open-type vessel is in a completely open state, and therefore the upper portion of a plant-supporting carrier is liable to be dried than the lower portion thereof so that aqueous or moisture condition in the vessel becomes ununiform and such a condition is liable to adversely affect the plant on the other hand, it is not usual to use a vessel having a closed-type lower portion. The reason for is that when the conventional vessel is simply used as one having a closed-type lower portion in combination with the conventional soil, the residence or retention of water becomes marked, and such a phenomenon is extremely liable to cause the above-mentioned insufficient oxygen supply, and root decay phenomenon due to the propagation of pathogens.
As described above, in the conventional plant-growing vessel or sheet, the environment of the rhizosphere is not suitable for the growth of a plant (inclusive of the germination of a seed and the growth thereof after the germination). Accordingly, when such a conventional vessel or sheet is used, there is required a complicated combination or regulation of the amount of water for the watering, the frequency of the watering, the concentration of solutions such as fertilizer, etc., and therefore the strict control of these factors has required great costs.
In general, with respect to various kinds of plant, the internal volume of the most suitable growing vessel has been known empirically depending on the kind, size thereof, etc. It is said that when the root of a plant is grown in soil so as to reach the wall of the growing vessel, the resultant mechanical contact stimulus promotes the origination of a new root. From such a viewpoint, the origination of root of the plant becomes better as the volume of the vessel becomes smaller. On the other hand, the internal volume of the vessel closely relates to the amount of water and nutrients stored therein which are to be supplied to the plant, and therefore, in general, the volume of the vessel of not lower than a certain level is required for the growth of the plant.
The circumstances of general cultivation farmhouses are those as described above. In recent years, however, in general homes, a many kinds of plant-growing vessels have been used in so-called xe2x80x9cprivate (vegetable) gardensxe2x80x9d. In general homes, since they do not have skilled experience or technique, unlike in the cultivation farmhouses, it is further difficult to suitably grow the plant, as compared with in the case of the cultivation farmhouses.
An object of the present invention is to provide a plant-cultivating support or a soil-modifying (or reforming) agent, which can solve the above-mentioned problems encountered in the prior art.
Another object of the present invention is to provide a plant-cultivating support or a soil modifying agent, which can suitably control the amount of water, the amount of nutrients, or the amount of a plant growth-regulating substance to be supplied to a plant so as to meet the demand of the plant, in accordance with a change in the external environmental factors such as temperature.
A further object of the present invention is to provide a plant-cultivating support or a soil modifying agent, which can enhance the productivity by saving labor to be required in open-air field cultivation and cultivation in facilities, and by reducing the facility costs.
A further object of the present invention is to provide a method of effectively growing a plant while using a plant-cultivating support or a soil-modifying agent.
A further object of the present invention is to provide a vessel or sheet for cultivating a plant, which can solve the above-mentioned problems of the conventional plant-cultivating vessel.
A further object of the present invention is to provide a plant-cultivating vessel or sheet, which can automate the transferring operation for a plant, and further can reduce the transferring damage to the plant at the time of the transferring operation.
A further object of the present invention is to provide a plant-cultivating vessel or sheet, which can suitably control the environment in the rhizosphere of the plant, while strict control of water, etc., is not necessarily required.
A further object of the present invention is to provide a plant-cultivating vessel or sheet, which has an ability to store water and/or nutrients which are necessary for the germination or growth of a plant.
A further object of the present invention is to provide a method of cultivating a plant, which has solved the above-mentioned problems encountered in the prior art.
A still further object of the present invention is to provide a method of cultivating a plant by using a support (or planting material) which can be used continuously from the culturing of the plant to the cultivation thereof.
As a result of earnest study, the present inventors have found that it is extremely effective in solving the above-mentioned problems to use a polymer which is capable of providing a hydrogel which has a crosslinked structure and shows a reversible change in a specific physical property, as a medium or a portion thereof (soil-modifying agent) for supporting a plant at the time of the cultivation of the plant.
The plant-cultivating support or soil-modifying agent according to the present invention is based on the above-mentioned discovery, and comprises: a hydrogel-forming polymer having a crosslinked structure and showing a decrease in the equilibrium water absorption thereof along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., the equilibrium water absorption being reversibly changeable with respect to temperature.
The present invention also provides a support for cultivating a plant, comprising, at least a carrier for supporting a plant; and a soil-modifying agent, comprising a hydrogel-forming polymer having a crosslinked structure and showing a decrease in the equilibrium water absorption thereof along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., the equilibrium water absorption being reversibly changeable with respect to temperature.
The present invention further provides a method of cultivating a plant, comprising:
disposing a plant-cultivating support at least around a plant; and
cultivating the plant while supporting the plant by the plant-cultivating support;
wherein the plant-cultivating support comprises a hydrogel-forming polymer-having a crosslinked structure a and shows a decrease in the equilibrium water absorption thereof along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., the equilibrium water absorption being reversibly changeable with respect to temperature.
The present invention further provides a method of cultivating a plant, comprising:
disposing a plant-cultivating support at least around a plant; and
cultivating the plant while supporting the plant by the plant-cultivating support;
wherein the plant-cultivating support comprises a plant-supporting carrier, and a soil-modifying agent added to the carrier in an amount of 0.1-10 wt., in terms of the weight in a dry state; the soil-modifying agent comprising a hydrogel-forming polymer having a crosslinked structure and showing a decrease in the equilibrium water absorption thereof along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., the equilibrium water absorption being reversibly changeable with respect to temperature.
As a result of further study based on the above discovery, the present inventors have also found that it is extremely effective in solving the problems in the prior art to dispose a polymer capable of providing a hydrogel having a crosslinked structure, in at least a portion of the internal surface of a vessel (e.g., bottom face and/or side face of the plant-growing vessel).
The vessel for growing a plant according to the present invention is based on the above discovery and comprises: a base material in the form of a vessel which is capable of accommodating therein at least a part of a plant; and a hydrogel-forming polymer disposed in the inside of the vessel-form base material; the hydrogel-forming polymer having a crosslinked structure.
The present inventors have also found that the effect of growing a plant may be obtained in the same manner as in the above-mentioned xe2x80x9cplant-growing vessel wherein a hydrogel-forming polymer is disposed in the inside thereofxe2x80x9d, even when a sheet-like material having the above-mentioned hydrogel-forming polymer disposed on a surface thereof is provided on an internal wall of the conventional plant-growing vessel.
The sheet for growing a plant according to the present invention is based on the above discovery, and comprises: a base material in the form of a sheet; and a hydrogel-forming polymer disposed on at least one of the surfaces of the sheet; the hydrogel-forming polymer having a crosslinked structure.
In the above-mentioned vessel or sheet according to the present invention, it is preferred that the hydrogel-forming polymer shows a decrease in the equilibrium water absorption thereof along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., the equilibrium water absorption being reversibly changeable with respect to temperature.
Further, in the present invention, when the hydrogel-forming polymer is in the form of powder or particles, the powder or particles may preferably have a dimension of 0.1 xcexcm-5 mm in a dry state.
As a result of further study, the present inventors have found that a gel-like support comprising at least water and a polymer capable of forming a hydrogel having a crosslinked structure exhibits a certain bacteriostatic (or bacteria growth-inhibiting) property, not only under an aeration (or ventilation)-restricted environment (at the time of culturing) but also under an aeration non-restricted environment (at the time of cultivation), on the basis of the characteristic of water disposed in the crosslinked structure of the gel. As a result of further study based on such a discovery, the present inventors have found that the gel-like support having a bacteriostatic property may be used as a support (or planting material) continuously, during the growth of a plant extending from the aeration-restricted environment to the aeration non-restricted environment.
The method of growing a plant according to the present invention is based on the above discovery, and comprises:
(a) culturing a plant under a ventilation-restricted condition by using a gel-type support comprising at least water and a hydrogel-forming polymer having crosslinked structure; and
(b) cultivating the plant under a ventilation non-restricted condition by using the gel-like support disposed in contact with the plant after the culturing, substantially as it is.
In the above-mentioned plant-growing method according to the present invention, the term xe2x80x9cusing a gel-like support substantially as it isxe2x80x9d means a state wherein the xe2x80x9cpositive or intentional removal operationxe2x80x9d for the gel-like support is not conducted with respect to the gel-like support attached to the plant after the culturing process, by using a measure or tool (e.g., removal operation using forceps, etc.) which can damage the plant. Accordingly, even in the present invention, at the time of the transfer from the culturing to the cultivation, it is permissible to conduct the natural or spontaneous dropping of the gel-like support from the plant, and the dropping of the gel-like support by lightly moving the root of the plant, etc.
In general, a plant is exposed to a temperature change in a night-and-day cycle of 24 hours, and a temperature change in a four-season cycle, not only in the open-air field cultivation but also in the facility cultivation. As described above, the demand of a plant for water, nutrients, a plant growth-regulating substance, etc., is increased when the temperature becomes higher, while such a demand of the plant is decreased when the temperature becomes lower. Accordingly, it is ideal that the watering, the supply of a fertilizer, the administration of a plant growth-regulating substance to a plant are conducted in response to the above-mentioned temperature change. However, not only in the open-air field cultivation but also in the facility cultivation, enormous costs are naturally required in order to conduct the watering, the supply of a fertilizer, and the administration of the plant growth-regulating substance to a plant in response to the above-mentioned temperature change.
On the contrary, the plant-cultivating support or soil-modifying agent according to the present invention can solve the above-mentioned problems on the basis of the function peculiar thereto as described below.
The plant-cultivating support or soil-modifying agent according to the present comprises a hydrogel-forming polymer wherein the equilibrium water absorption is decreased along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than of 70xc2x0 C., and the change in the equilibrium water absorption is reversible with respect to the temperature. Accordingly, in the above predetermined temperature range (temperature range of not lower than 0xc2x0 C. and not higher than of 70xc2x0 C.), as the temperature becomes higher, the volume of the hydrogel comprising such a polymer is decreased, and on the basis of the volume decrease, the hydrogel discharges the water, nutrients, and/or plant growth-regulating substance contained in the inside of the hydrogel to the outside of the hydrogel (or, into another carrier such as soil), thereby to cause these substances to be in a state wherein they are liable to be easily absorbed into the plant through the root thereof. On the other hand, when the temperature becomes lower and the demand of the plant for the water, nutrients, and growth-regulating substance is decreased, the hydrogel (or hydrogel-forming polymer) absorbs these substances which are present in the outside of the hydrogel or in another carrier (such as soil), into the hydrogel per se, and stores these substances them in the hydrogel. Accordingly, an excess amount of these substances are not present in the outside of the hydrogel (or in another carrier such as soil), thereby to effectively suppress the adverse effect on the plant based on the presence of an excess amount of these substances.
The effect of the application of the support for a plant and soil-modifying agent according to the present invention may be exhibited more suitably under an environment wherein the xe2x80x9cwater content stressxe2x80x9d to a plant is strong (e.g., desert, ground surface after tearing-off operation, building surfaces, roof and inside of buildings, etc.).
The support according or soil-modifying agent according to the present invention is concerned with the growth of a plant per se, and therefore it is suitably applicable to the development of lawn, greening of an atrium (an open-air courtyard in the inside of a building), virescence of desert, virescence of slopes, virescence of rooftops, virescence of wall surfaces, etc. Even when the support or soil-modifying agent according to the present invention is sprayed on the slope or wall surface, etc., together with a seed, the water content in the neighborhood of the seed is suitably be controlled with respect to the temperature change in the above-described manner, whereby the germination thereof is promoted and the growth thereof after the germination is also promoted, and the virescence of the slope, etc., is conducted extremely smoothly. Further, even when only the support or soil-modifying agent (containing no seed) according to the present invention is sprayed on the wall or slope surface, etc., the ecesis or establishment of seeds which spontaneously fall onto the wall surface, etc., the germination thereof, or the growth thereof after the germination is promoted, and the virescence of the wall surface, etc., is conducted smoothly.
Then, there is described the vessel or sheet according to the present invention
As described above, most of the operations required for the germination or growth of a plant using a vessel in the tissue culturing or farm cultivation, are dependent on human labor. Particularly, the transferring operation of a plant conducted by manual operations not only requires a long period of time, but also it causes some damage to the plant.
More specifically, at the time of such a transfer operation, the thickly grown root of the plant presses the wall surface of the vessel so as to cause a friction therewith, and therefore a considerable period of time is required in order to take out the plant from the vessel, and the plant per se is damaged in many cases. In addition, when the plant is transferred to a vessel for receiving the plant after such a vessel is filled up with a solid plant-supporting carrier, the root of the plant does not enter the inside of the carrier well, and therefore the productivity or workability in the transfer operation is decreased, and the root per se is also damaged in many cases. Further, at the time at which a plant having an elongated root is intended to be transferred, even when the plant is implanted into the vessel after the plant is covered with a carrier for retention thereof (e.g., peat-moss) in advance, the transfer operation still requires a considerable period of time. Further, even when the plant is first put into the vessel and thereafter a granule-like plant-supporting carrier is charged into the vessel, the initial growth of the plant is poor in many cases. According to the present inventors"" knowledge, it is presumably considered that such poorness in the initial growth is attributed to a small contact area between the root of the plant and the plant-supporting carrier.
On the contrary, when the plant-growing vessel or sheet according to the present invention is used, the above-mentioned problem encountered in the prior art may be solved on the basis of the function peculiar to the vessel or sheet according to the present invention as described hereinbelow.
More specifically, a polymer capable of providing a hydrogel having a crosslinked structure is disposed on the inner wall of the plant-growing vessel according to the present invention (or on the side of the sheet according to the present invention, on which a plant is to be disposed, when such a sheet is disposed on the inner wall of another vessel) by coating, etc. Accordingly, when the plant is put into the vessel and then the vessel is filled with water or a liquid culture medium, the above-mentioned hydrogel-forming polymer absorbs water so that the volume thereof is increased remarkably, and occupies the inner space of the vessel, whereby the polymer functions as at least a part of the support for the plant (in other words, the hydrogel-forming polymer functions as such a support, or promotes the supporting function for the plant).
In the present invention, on the basis of the function peculiar to the above-mentioned xe2x80x9cpolymer capable of providing a hydrogel having a crosslinked structurexe2x80x9d, the problems encountered in the prior art are solved. More specifically, such problems to be solved may include: one such that when a plant is transferred into a vessel after the vessel is filled with a solid plant-supporting carrier in advance, the root of the plant does not enter the inside of the carrier well, and therefore the resultant workability is decreased, and the root per se is also damaged; one such that when a plant is put into a vessel and then the conventional solid plant-supporting carrier is charged into the vessel, the resultant initial growth is decreased due to a small contact area between the root of the plant and the carrier; etc.
In addition, in an embodiment of the present invention wherein the hydrogel-forming polymer to be disposed on the inner wall of the vessel by coating comprises a hydrogel-forming polymer wherein the equilibrium water absorption is decreased along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., and the change in the equilibrium water absorption is reversible with respect to temperature, for example, it is possible that a plant is put into such a vessel, water or a liquid culture medium is poured into the vessel so that the polymer is caused to absorb water, whereby the polymer is swollen so as to occupy the inner space of the vessel and the plant is grown by using the polymer as (at least a part of) the support of the plant. After the plant is grown, when the temperature of the support is elevated, the hydrogel-forming polymer is de-swelled (or shrunk) so as to markedly decrease its volume, and therefore the grown plant may easily be removed from the vessel.
Accordingly, the present invention solves the above-mentioned problem encountered in the prior art, i.e., one such that since the thickly grown root presses the wall surface of the vessel, a considerable period of time is required in order to take out the plant from the vessel, and such an operation damages the root.
Another serious problem in the conventional plant-growing vessel is, as described above, that the environment in the rhizosphere is not suitable for the growth of the plant. Particularly, in close relation with the material of the vessel, the neighborhood of the inner wall of the vessel has a tendency such that the water content in this region is liable to be excessive or deficient, and further the difference in temperature (hot or cold) is large due to the influence of external air temperature. In general, the density of the growing root is particularly high in the neighborhood of the vessel wall, and such an adverse environment in the rhizosphere is liable to adversely affect the growth of the plant remarkably. Further, the bottom portion of the vessel is particularly liable to assume a water-excessive state due to watering, and on the contrary, the upper portion of the vessel is liable to assume a water-deficient state. Both of these water-excessive and water-deficient states adversely affect the growth of the plant.
On the contrary, the plant-growing vessel or sheet according to the present invention having the above-mentioned structure can solve the above-mentioned problems on the basis of the function peculiar to such a vessel or sheet, as described hereinbelow.
A polymer capable of providing a hydrogel having a crosslinked structure is disposed on the sheet or inner wall of the vessel according to the present invention by coating, etc. When the support (such as soil) in the neighborhood of the inner wall of the vessel assumes a water-excessive state for the above-mentioned reason, the polymer absorbs water so as to assume a hydrogel state. On the other hand, when the support in the neighborhood of the inner wall of the vessel assumes a water-deficient state, the hydrogel particles have a function of transferring water therefrom into the support. As a result, the environment for water in the thizosphere in the neighborhood of the inner wall of the vessel is maintained almost constant, and the problems encountered in the prior art are solved.
Particularly, in an embodiment of the present invention wherein the above hydrogel-forming polymer comprises a hydrogel-forming polymer wherein the equilibrium water absorption is decreased along with an increase in temperature in the temperature range of not lower than 0xc2x0 C. and not higher than 70xc2x0 C., and the change in the equilibrium water absorption is reversible with respect to temperature, the polymer absorbs water from the support when the temperature becomes lower, while the polymer discharges water into the support when the temperature becomes higher. In other words, the water content in the support in the neighborhood of the sheet or the wall of the vessel is increased as the temperature becomes higher. In general, it is considered that a plant demands a smaller amount of water when the temperature is low (below about 5-20xc2x0 C.), and demands a larger amount of water as the temperature becomes higher (not lower than about 20-35xc2x0 C.). It is also considered that the excessive water content at a lower temperature invites a root decay phenomenon, and the deficient water content at a higher temperature invites insufficient growth. Accordingly, when the above-mentioned vessel or sheet having a hydrogel-forming polymer disposed therein is used, the environment in the rhizosphere is maintained more suitably, thereby to promote the growth of the plant more effectively.
In addition, the hydrogel-forming polymer disposed on the inner wall of the plant-growing vessel (or on the sheet to be disposed on the inner wall of the vessel) has a function of storing water content and/or nutrients in the crosslinked structure of the polymer as described above. Therefore, the storing function which has been performed by the xe2x80x9cspacexe2x80x9d in the conventional growing vessel, may be performed by the above polymer extremely effectively in place of the above space. Therefore, according to the present invention (even when the ability of the growing vessel for storing water content and nutrients is retained constant), the internal volume of the vessel can be reduced remarkably.
As described above, according to the present invention, the volume of a vessel which has been considered to be xe2x80x9cappropriatexe2x80x9d in the prior art can be reduced remarkably, and further the originating power of the root can be improved due to an increase in the opportunity for the mechanical contact stimulus. Further, on the basis of the reduction in the internal volume of the vessel per se, it is also possible to reduce the area to be used for growing a plant, to reduce the amount of the material for the growing vessel, and to reduce the transporting costs. In addition, in combination with the above-mentioned labor saving in the water control, remarkable cost reduction can be accomplished.
Further, since the conventional vessel for home use has a lower portion of an open-system, and an excess of water is discharged from the open-system lower portion at the time of the watering, etc., a xe2x80x9creceiving panxe2x80x9d must be used simultaneously therewith. The use of such a pan is troublesome and it is liable to impair the beautiful appearance thereof.
On the contrary, in the plant-growing vessel according to the present invention, since the water-storing ability is imparted to the wall surface of the vessel, it is not necessarily required to provide an opening portion at a lower part of the vessel. In other words, the opening portion of the vessel is omissible in the present invention. When the vessel having a closed-type lower portion is used, the problems encountered in the conventional vessel for home use (having an open-system lower portion) are easily solved.
In the above, the growth of a plant after the germination thereof has mainly been described, but the vessel or sheet according to the present invention is also suitably applicable to the germination of a seed or the growth thereof after the germination.